1. Field of the Invention
The present invention relates to a continuous firing equipment and, more particularly, it relates to a furnace for continuously firing ceramics and like products.
2. Description of the Prior art
In the manufacture of ceramics and like products, there have widely been used tunnel kilns having a cunstruction as shown in FIG. 1, wherein a sagger 2 in which ware to be fired have been placed is loaded on a ceramic tray 1, and it is then moved on a track 7 from the point of feed through a chamber 5 of a furnace 4 to the point of discharge by means of a pusher 3. The ceramic tray 1 used in such firing process must be strong enough to resist the pressure applied by the pusher 3, it is necessary to construct the tray so as to have a high mechanical strength. To that end, the ceramic tray 1 must be made thicker. Consequently, the heat capacity of the tray becomes considerably large and the amount of heat needed to heat the tray 1 becomes large as compared with the heat needed to heat the ware to be fired. This results in a considerable increase of the heat lost by the trays and in lowering of the temperature gradient in the furnace. This necessarily causes an increase in the length of the furnace and in the firing time. In addition, the trays have generally been made of a ceramic material such as alumina, zirconia, fire brick, insulating brick and the like that has a low resistance to thermal shocks, so that they impose restrictions on the heating rate and the cooling rate of the ware, thus making it impossible with such trays to fire the ware that requires the rapid heating and the rapid cooling. Since the trays are moved intermittently, it is not possible to achieve continuous firing of the ware to be fired. For the reasons mentioned above, it takes a long time to fire the ceramic ware. For example, the firing of the ceramic ware takes about 16 hours since the heating rate and the cooling rate have been restricted to about 200.degree. C./hour at the maximum.
On the other hand, it has been desirable to develop new firing equipment for tunnel kilns, due to the significant increases in the cost of energy as well as a great demand for the reduction of the firing time.